The advent of digital recording techniques has enabled digital copies of digital content carried by recording media such as optical discs (for example DVDs) to be made with little or no loss of copy quality. This makes it easy for an unauthorised person to produce unauthorised copies of digital content-carrying recording media. Accordingly, copy-protection techniques have been developed. One copy protection technique that is currently used to protect the content of DVDs from digital copying is the proprietary Content Scrambling System (CSS) in which some frames or sectors containing audio, video or sub-picture data of a video title set are scrambled and encrypted using a combination of a title key and a disc key. The title key is stored in the sector header and the disc key is stored in a control area of the disc which is not accessible to a player that does not have a CSS decryption module. Each CSS-protected DVD also includes a list of player keys to enable identification of players licensed under the CSS system. When a CSS-protected disc is inserted into a CSS-licensed player, a CSS decryption module of the player exchanges player keys with the disc and, if the player key of the player matches one of the player keys in the list carried by the disc, an encryption key is generated from the player keys for use in encrypting the transfer of the disc and title keys to the player to enable the CSS decryption module to decrypt the CSS encrypted sectors. Encrypting the transfer of these keys inhibits interception of the transferred data. An unlicensed player, that is a player without the CSS decryption module (or a player without a legitimate player key) will not be able to decrypt the CSS encrypted sectors and so at least part of the content of the DVD will not be playable. This copy-protection system requires both the producer of the recorded medium and the producer of the player of the recorded medium to be licensed to implement the CSS protection system. Similar considerations apply to other proprietary protection systems.